Abstract [en]

In response to pain, neurokinin 1 (NK1) receptor availability in the central nervous system is altered in the dorsal horn of the spinal cord as well as in the brain. But the NK1 receptor and its primary agonist, substance P, also play a crucial role in peripheral tissue in response to pain, as part of neurogenic inflammation. However, little is known about alterations in NK1 receptor availability in peripheral tissue in chronic pain conditions and very few studies have been performed on human beings. We therefore performed positron emission tomography (PET) with the NK1 specific radioligand [11C]GR205171 in ten subjects with chronic tennis elbow. We demonstrated increased NK1 receptor availability in the affected arm as compared with the unaffected arm, measured as differences between the arms in number and volume of pixels > 2.5 SD above reference as well as signal intensity of this volume. We conclude that in addition to alteration of the NK1 receptor in the CNS, there is also activation, or up-regulation of the NK1 receptor in the peripheral, painful tissue in a chronic pain condition. We interpret this increased NK1 receptor availability as part of ongoing neurogenic inflammation and suggest that this is part of the cause of chronic tennis elbow.

Peterson, Magnus

Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Family Medicine and Clinical Epidemiology.

2011 (English)Doctoral thesis, comprehensive summary (Other academic)

Abstract [en]

Objectives: To study the treatment practice of chronic tennis elbow (TE) among general practitioners (GPs) and physiotherapists (PTs), the effects of a simple, graded home exercise regime versus expectation, the effects of eccentric versus concentric exercise, and the involvement of the substance P – NK1 receptor system in the peripheral, painful tissue of chronic TE patients by positron emission tomography (PET).

Materials and methods: A postal survey regarding therapeutic methods used in patients with chronic TE was sent to 129 GPs and 77 PTs, 81 subjects with chronic TE were randomly and blindlyassigned to either an exercise group or a wait list group, 120 subjects were randomly assigned to either eccentric or concentric exercise and ten subjects were examined by PET and the NK1 specific radioligand [11C]GR205171.

Results: High proportions of GPs and PTs used ergonomic counselling and stretching in the treatment of chronic TE. The majority of GPs prescribed passive anti-inflammatory measures such as sick leave and anti-inflammatory medication. Many PTs prescribed dynamic, particularly eccentric, exercise.Graded dynamic exercise according to a simple low-cost protocol, has better effect on pain than a wait-and-see attitude. Adjusted for outcome affecting variables, eccentric graded exercise has quicker effect than concentric graded exercise. During PET scan with the NK1 specific radioligand [11C]GR205171, voxel volume and signal intensity of this volume was significantly higher in the affected than the unaffected arm in subjects with unilateral chronic TE.

Conclusions: GPs and PTs used many treatments to a similar extent but differed regarding the use of exercise. Chronic TE responds favourably to graded dynamic exercise aimed specifically at the painful tissue. The exercise should stress the eccentric work phase. The substance P – NK1 receptor system seems to play a part in the peripheral, painful tissue of a chronic, soft tissue pain condition such as chronic TE.